Corner reflector antenna



Feb. 28, 1961 J. H. JENSEN CORNER REFLECTOR ANTENNA 3 Sheets-Sheet 1Filed Sept. 25, 1957 INVENTOR. JACK H. JENSEN ATTORNEYS Feb. 28, 1961 J.JENSEN CORNER REFLECTOR ANTENNA 3 Sheets-Sheet 2 Filed Sept. 25, 1957Fig. 6

IN V EN TOR.

s 5 Y m f J .M H In W 4 M Feb. 28, 1961 J. H. JENSEN 2,973,518

CORNER REFLECTOR ANTENNA Filed Sept. 25, 1957 5 Sheets-Sheet S VERTICALPATTERN HORIZONTAL PATTERN INVENTOR. J4 CK H. JENSEN CORNER REFLECTORANTENNA Jack H. Jensen, 333 Westwind Drive, San Diego, Calif.

Filed Sept. 25, 1957, Ser. No. 686,266

6 Claims. (Cl. 343-837) (Granted under Title 35, US. Code (1952), see.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor. 4

The present invention relates to a corner reflector antenna and moreparticularly to an improved corner reflector antenna for radiating adirectional type beam having a controllable beam tile.

My co-pending application Serial No. 649,576, filed March 29, 1957, nowPatent No. 2,926,349 issued February 23, 1960, discloses a cornerreflector antenna for radiating a directional type radar beam of anapproximate 35 elevation. In using this antenna where a horizontal typebeam is desired, it is necessary to tilt the whole antenna structureforward to an angle of an approximate 35. It is readily apparent that inmany uses of the corner antenna, an antenna capable of being mounted ina horizontal position and yet radiate a horizontal beam is desirable.This is especially true when the antenna is mounted upon a rotatablepedestal.

The present invention is an improvement upon my prior corner reflectorantenna in that it provides structural improvements which allow theantenna to project a directional type beam in a horizontal directionwhen the antenna is mounted upon a pedestal in a horizontal position,and further the invention permits the tilt of the directional beam to beselectively varied.

An object of the present invention is the provision of a cornerreflector antenna having a directional type beam radiated in ahorizontal direction relative to its finite ground plane.

Another object is to provide a corner reflector antenna with a beamhaving selective elevations.

A further object of the invention is the provision of a corner reflectorantenna that radiates a directional type beam stabilized in a horizontaldirection relative to its finite ground plane over a desired range offrequencies.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. 1 shows a perspective view partly broken away of a preferredembodiment of the invention;

Fig. 2 discloses a top plan view of the apparatus;

Fig. 3 shows a top plan view of the antenna with the reflector unitremoved;

Fig. 4 shows a section of the antenna and pedestal with the reflectorunit removed taken on line 4-4 of Fig. 3 looking in the direction of thearrows;

Fig.5 is a diagrammatical end view of a parabolic cylinder illustratingthat part of the cylinder from which Patented Feb. 28, 1961 ice Fig. 8illustrates graphically the characteristics of the directional beam inthe horizontal azimuth.

Referring now to the drawings, wherein like reference charactersdesignate like or corresponding parts throughout the several views,there is shown in Fig. l a parabolic corner reflector antenna 9 mountedon a swivel topped pedestal 18. The reflector portion of the antenna hastwo parabolic members 10 joined at substantially a angle by soldering orthe like and Secured to plate 13 in a similar manner. Plate 13 providesadded structural strength to the parabolic members in their mountedposition, provides a horizontal attaching means for securing the membersto the pedestal 18 and also cooperates with reflecting surfaces 23 inradiating and receiving radar energy. It is within the scope of theinvention to not join the parabolic members together as shownin Figs. 1and 2. The members may be separated at the corner of intersection aslong as they are held at substantially a right angle and the corner endspositioned in close proximity. The allowable separation between the endsdepends upon the parameters of the antenna and the effect the degree ofseparation has on the pattern. This latter elfect may be determined byexperiment and it was found that the pattern characteristic became lessdesirable as the separation at the corner was increased. This result isevident as there will be radiation leakage through the gap causingincreased losses to the rear of the antenna. I

Parabolic members 10 are symmetrical sections of a parabolic cylinderpartially illustrated schematically in Fig. 5 as line 27. The cylindersection has the usual curvature formula of y equals 4fx, for the Originat the vertex. The cylinders focal line 28 lies on the parabolas axisline 29. Parabolic member 10 used in the reflector array was removedfrom cylinder 27 as shown with its lower edge at the center point 30* ofthe parabolic cylinder. The members may be constructed of aluminum orthe like or by light-weight fabrication techniques such as roddedconstruction or fiber glass honey-comb construction with important partsmetal sprayed.

Plate 13 has a forward part 14 (see Figs. 1 and 2) that for-ms the soleof the reflecting unit. Sole 14 has a lip 15 that is downwardly inclinedat an acute angle and has an arcuate edge, the radius of which generallyextends from the radiator. The purpose of sole 14 and lip 15 will beexplained in detail later.

Referring to Fig.4 ground plane member 12 is a radial extension of theouter conductor member 21 of the coaxial line that feeds high frequencycurrent to radiator 11, and is supported at its outer edge by shoulder33 of cylindrical member 30. The surface area of the ground plane member12 is not critical as long as its area is suflicient to form an adequatesupport for ring 17 and the reflecting unit, and as long as it providesa ground plane surface surrounding radiator 11 that is sufiicient toclose the immediate area between the parabolic members and thus reduceradiation leakage below the radiator. A circular bearing member 25 isattached to the upper and outer portion of cylinder 30 and supports rimstructure 26 for free rotational movement relative to the cylinder 30and ground plane member 12.

Ring 17 is mounted on rim 26 by means of screws as shown in Fig. 4.Plate 13 and sole 14 are fixed to ring 17 in a similar manner. Thisstructural arrangement permits rotational movement by the reflector uniton pedestal 18. Ring 17 is spaced from the ground plane member 12 atpoints where the ring 17 overlaps the ground plane 12 such as at 31 inFig. 4. For reasons to be explained in detail later, a capacitive effectbetween ring 17 and ground plane member 12 is necessary to the operationof the antenna. In the specific embodiment this capacitive effect isprovided by the space between rim 26 and side in the following manner.

member 30 through bearing 25. Rim 26 is electrically connected to ring17 and side member 30 is directly connected electrically to the groundplane member. Should the rotational feature of the antenna-pedestalcombination not be desired, the hearing may be omitted and rim 26 andground plane member 12 made integral. The required capacitive effect canthen be provided by a thin layer of insulation between rim 26 and ring17.

Radiator 11, in the preferred embodiment, is of the fat-door-knobmonopole type. However, it may be one of other suitable types known inthe art. It is insulated from the ground plane member 12 and spacedabove it, see Fig. 4, an amount dependent upon the height at whichoptimum impedance matching is obtained. Once optimum impedance matchingis obtained, small movement of the radiator vertically will notappreciably affect the pattern. The radiator is positioned horizontallybetween the parabolic members on a line bisecting the angle ofintersection of the members.

Sole 14 and its lip 15 serve in the antenna structure as the finiteground plane which lowers the tilt of the beam radiated from the antennaunit to a horizontal direction If a flat, finite ground plane is usedwithout a lip portion, high frequency waves radiated from the radiatorand reflectors will travel along the upper surface of the finite groundplane. Upon reaching the outer edge of the finite ground plane a portionof the radiated waves will encompass the edge thereof and cause highfrequency waves to travel in a direction toward the radiator andreflectors via the under surface of the finite ground plane. The actionof the radiated waves in encircling the finite ground planes edgeresults in a cancellation effect on that portion of the total radiatedbeam that is immediately adjacent the upper surface of the finite groundplane. This cancellation effect creates an effective beam that is tiltedupwardly relative to the finite ground plane. For example, in myco-pending application, there is disclosed therein an antenna utilizinga flat, finite ground plane without a lip portion that transmits apencil type beam tilted upwardly 35 relative to the ground plane.

The addition of lip 15 to sole 14 transfers the rolling over the edgeeffect of the radiated waves from the sole member to the edge of the lipportion. Thus the lip portion functions as the edge portion of finiteground plane in this circumstance and the beam is tilted upwardly fromthe lip portion rather than from sole 14. Inasmuch as the lip portion isangled downwardly relative to the sole,

the resultant radiated beam is projected in a direction horizontal tothe fiat surface portion'of sole 14.

In operation of the antenna, a change in frequency'of the radiated waveswill cause a change in the tilt of the beam. To provide increasedstability of the beam tilt and allow a broader range of frequencies tobe transmitted, ring 17 was incorporated into the antenna structure.

Ring 17 is spaced from the ground plane member 12 providing a capacitiveeflect therebetween. This capacitive effect is obtained in the specificembodiment by adjacent positioning of ring 17 and ground plane member 12as at 31 in Fig. 4, and the spacing between members in ring bearings 25.The spacing of elements 12 and 17 through bearing 25 forms an RF chokejoint, which prevents ring 17 from being electrically shorted to groundplane member 12. The impedance presented by this arrangement varies dueto the varying width of ring 17. The exact theory of operation is notentirely understood. The capacitive effect plus the spacing of plate 13of the radiating unit from the ground plane member 12 by ring 17,functions to correlate the phase of the current passing from the outerconductor 21 to the reflecting members and to sole 14 and lip 15.

Ring 17, see Fig. 3, is asymmetrical having a circular outer edge withan off-set circularhole 32 therein. The off-set center space allows oneside A to be of greater width than the opposite side 13. The widerportion A 4 may be positioned on either the front or rear side of thereflector unit depending upon the parameters of the reflecting unitsused. In the specific embodiment side A is positioned on the rear sideof the antenna.

The radiated r-adar beam may be maintained steadily in a horizontalposition or it may be selectively raised or lowered through movement ofthe ring or parts thereof. Disk 17 is electrically connected to thereflector unit and while it may be fixed thereto or made integraltherewith in a position that will hold the beam tilt to a horizontalposition; to facilitate selective raising or lowering the tilt of thebeam, the disk can also be made slidable relative to the reflector unit.This latter construction allows the ring to be moved forwardly orrearwardly relative to the reflecting unit and pedestal, causing aregulated lowering or raising of the beam tilt.

An alternative method of controlling the beam is to slidably move only asection 24 from ring 17, as shown in Fig. 6. In this manner the mainbody of ring 17 may be permanently secured to the antenna structure andthe lowering or raising of the beam accomplished by sliding section 24toward or away from the radiator 11.

Ring 17 may be considered a vernier to the sole 14 and its lip 15 incontrolling the tilt of the beam and stabilizing it. Also the V-shapedspace 22 (see Figs. 1- and 2) between the upper edges of the parabolicmembers functions to stabilize the beam as a further impedance mis-matchcorrection factor.

Slot 19 in sole 14 has no effect on the pattern but merely providesmeans for variably positioning parasitic director 16. The director ismoved in the slot experimentally to a position giving the patterncharacteristic desired. It serves a useful adjunct to the antenna as itincreases gain and decreases the side lobes and may be eitherelectrically connected to the outer conductor, as in the specificembodiment, or it may be insulated therefrom or suspended in space withrespect thereto. The same pattern will result regardless of the methodof support adopted. However, if the director is suspended or insulated,then a slight adjustment in its position relative to the radiator andreflector is necessary to obtain the optimum pattern. This adjustment isnecessary to com pensate for the capacitance effect that would arise.

The directional characteristic obtainable with the parabolic cornerreflector of this invention are illustrated graphically in Figs. 6 and7. These curves represent the characteristics of the beam wave invertical and horizontal azimuth plane for a frequency of 8800 me. andillustrate the pencil type beam obtained.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. In an antenna, reflector means for transmitting or receivingdirectional high frequency waves including two parabolic members alignedin substantially a V-shape and finite ground plane means positionedbetween said members at their bottom edges for radiating and receivingsaid waves in coordination with said parabolic members, other groundplane means positioned in reactive relationship with said finite groundplane means for opposing radiation leakage below the bottom of saidparabolic members.

2. In an antenna, reflector means for transmitting or receiving adirectional high frequency beam including two parabolic members alignedin substantially a V-shape, ground plane means positioned below saidparabolic members, said reflector means having finite ground plane meanspositioned between-said members at their bottom edges for projectingsaid radiated beam in a direction horizontal to said finite ground planemeans and said ground plane means and reactive means positioned betweensaid finite ground plane means and said ground plane means forstabilizing said beam in said horizontal direction.

3. The combination of claim 2, wherein said reactive means comprises aring member electrically connected to said parabolic members and saidfinite ground plane means and spaced from said ground plane means givinga capacitive efiect therebetween.

4. In the combination of claim 3, wherein said ring member includes aremovable section for selectively varying the elevational tilt of saidbeam relative to said finite ground plane means and said ground planemeans, said section being slidable relative to said finite ground planemeans and said ground plane means whereby said reactive efiect isvariable.

5. In an antenna, reflector means for transmitting or receiving adirectional high frequency beam including two parabolic members alignedin substantially a V-shape, ground plane means positioned below saidparabolic members, said reflector means having finite ground plane meanspositioned between said members at their bottom edges for projectingsaid radiated beam horizontally to said finite ground plane means andconductive ring slidably positioned between said finite ground planemeans and said ground plane means for selectively varying theelevational tilt of said beam, said conductive ring being electricallyconnected to said parabolic members and said finite ground plane meansand spaced from said ground plane means permitting a capacitive effecttherebetween.

6. In an antenna, reflector means for transmitting or receiving adirectional high frequency beam including two parabolic members alignedin substantially a V-shape and finite ground plane means positionedbetween said conductive ring positioned between said finite ground planemeans and said ground plane means and encircling said radiator, saidconductive ring being electrically connected to said parabolic membersand said finite ground plane means and spaced from said other groundplane means permitting a capacitive effect therebetween.

References Cited in the file of this patent UNITED STATES PATENTS1,781,046 Bethenod Jan. 23, 1934 1,944,563 Kruesi Jan. 23, 19342,408,373 Chu Oct. 1, 1946 2,421,988 Brown June 10, 1947 2,436,408Tawney Feb. 24, 1948 2,534,710 Golian et a1 Dec. 19, 1950 2,567,746 VanAtta Sept. 11, 1951 2,594,871 Chu et al Apr. 29, 1952 2,600,274 SichakJune 10, 1952 2,615,132 Rumsey Oct. 21, 1952 2,836,820 Pickles et al May27, 1958 FOREIGN PATENTS 522,682 Germany Apr. 13, 1931 OTHER REFERENCESAntennas, by Kraus, copyright 1950, page 338.

